Index: trunk/src/org/openstreetmap/josm/data/cache/JCSCachedTileLoaderJob.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/cache/JCSCachedTileLoaderJob.java	(revision 14532)
+++ trunk/src/org/openstreetmap/josm/data/cache/JCSCachedTileLoaderJob.java	(revision 14535)
@@ -420,5 +420,11 @@
     }
 
-    protected String detectErrorMessage(String data) {
+    /**
+     * Tries do detect an error message from given string.
+     * @param data string to analyze
+     * @return error message if detected, or null
+     * @since 14535
+     */
+    public String detectErrorMessage(String data) {
         Matcher m = HttpClient.getTomcatErrorMatcher(data);
         return m.matches() ? m.group(1).replace("'", "''") : null;
Index: trunk/src/org/openstreetmap/josm/data/imagery/TMSCachedTileLoaderJob.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/imagery/TMSCachedTileLoaderJob.java	(revision 14532)
+++ trunk/src/org/openstreetmap/josm/data/imagery/TMSCachedTileLoaderJob.java	(revision 14535)
@@ -67,5 +67,4 @@
      * @param downloadExecutor that will be executing the jobs
      */
-
     public TMSCachedTileLoaderJob(TileLoaderListener listener, Tile tile,
             ICacheAccess<String, BufferedImageCacheEntry> cache,
@@ -321,5 +320,5 @@
 
     @Override
-    protected String detectErrorMessage(String data) {
+    public String detectErrorMessage(String data) {
         Matcher m = SERVICE_EXCEPTION_PATTERN.matcher(data);
         return m.matches() ? removeCdata(Utils.strip(m.group(1))) : super.detectErrorMessage(data);
Index: trunk/src/org/openstreetmap/josm/io/AbstractReader.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/AbstractReader.java	(revision 14532)
+++ trunk/src/org/openstreetmap/josm/io/AbstractReader.java	(revision 14535)
@@ -14,4 +14,5 @@
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.OptionalLong;
 import java.util.function.Consumer;
 
@@ -323,4 +324,8 @@
             throw new IllegalDataException(e);
         } finally {
+            OptionalLong minId = externalIdMap.values().stream().mapToLong(AbstractPrimitive::getUniqueId).min();
+            if (minId.isPresent() && minId.getAsLong() < AbstractPrimitive.currentUniqueId()) {
+                AbstractPrimitive.advanceUniqueId(minId.getAsLong());
+            }
             progressMonitor.finishTask();
             progressMonitor.removeCancelListener(cancelListener);
@@ -604,10 +609,21 @@
     }
 
+    @SuppressWarnings("unchecked")
+    private <T extends OsmPrimitive> T buildPrimitive(PrimitiveData pd) {
+        OsmPrimitive p;
+        if (pd.getUniqueId() < AbstractPrimitive.currentUniqueId()) {
+            p = pd.getType().newInstance(pd.getUniqueId(), true);
+        } else {
+            p = pd.getType().newVersionedInstance(pd.getId(), pd.getVersion());
+        }
+        p.setVisible(pd.isVisible());
+        p.load(pd);
+        externalIdMap.put(pd.getPrimitiveId(), p);
+        return (T) p;
+    }
+
     private Node addNode(NodeData nd, NodeReader nodeReader) throws IllegalDataException {
-        Node n = new Node(nd.getId(), nd.getVersion());
-        n.setVisible(nd.isVisible());
-        n.load(nd);
+        Node n = buildPrimitive(nd);
         nodeReader.accept(n);
-        externalIdMap.put(nd.getPrimitiveId(), n);
         return n;
     }
@@ -615,5 +631,5 @@
     protected final Node parseNode(double lat, double lon, CommonReader commonReader, NodeReader nodeReader)
             throws IllegalDataException {
-        NodeData nd = new NodeData();
+        NodeData nd = new NodeData(0);
         LatLon ll = null;
         if (areLatLonDefined(lat, lon)) {
@@ -654,10 +670,7 @@
 
     protected final Way parseWay(CommonReader commonReader, WayReader wayReader) throws IllegalDataException {
-        WayData wd = new WayData();
+        WayData wd = new WayData(0);
         commonReader.accept(wd);
-        Way w = new Way(wd.getId(), wd.getVersion());
-        w.setVisible(wd.isVisible());
-        w.load(wd);
-        externalIdMap.put(wd.getPrimitiveId(), w);
+        Way w = buildPrimitive(wd);
 
         Collection<Long> nodeIds = new ArrayList<>();
@@ -672,10 +685,7 @@
 
     protected final Relation parseRelation(CommonReader commonReader, RelationReader relationReader) throws IllegalDataException {
-        RelationData rd = new RelationData();
+        RelationData rd = new RelationData(0);
         commonReader.accept(rd);
-        Relation r = new Relation(rd.getId(), rd.getVersion());
-        r.setVisible(rd.isVisible());
-        r.load(rd);
-        externalIdMap.put(rd.getPrimitiveId(), r);
+        Relation r = buildPrimitive(rd);
 
         Collection<RelationMemberData> members = new ArrayList<>();
Index: trunk/src/org/openstreetmap/josm/io/CachedFile.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/CachedFile.java	(revision 14532)
+++ trunk/src/org/openstreetmap/josm/io/CachedFile.java	(revision 14535)
@@ -5,5 +5,4 @@
 
 import java.io.BufferedReader;
-import java.io.ByteArrayOutputStream;
 import java.io.Closeable;
 import java.io.File;
@@ -245,14 +244,5 @@
      */
     public byte[] getByteContent() throws IOException {
-        try (InputStream is = getInputStream()) {
-            ByteArrayOutputStream buffer = new ByteArrayOutputStream();
-            int nRead;
-            byte[] data = new byte[8192];
-            while ((nRead = is.read(data, 0, data.length)) != -1) {
-                buffer.write(data, 0, nRead);
-            }
-            buffer.flush();
-            return buffer.toByteArray();
-        }
+        return Utils.readBytesFromStream(getInputStream());
     }
 
Index: trunk/src/org/openstreetmap/josm/tools/Utils.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/Utils.java	(revision 14532)
+++ trunk/src/org/openstreetmap/josm/tools/Utils.java	(revision 14535)
@@ -1447,5 +1447,5 @@
         try {
             ByteArrayOutputStream bout = new ByteArrayOutputStream(stream.available());
-            byte[] buffer = new byte[2048];
+            byte[] buffer = new byte[8192];
             boolean finished = false;
             do {